 So another way of looking at subtraction is an approach called equal add-ins. And this emerges from the following. If we go back to our tape diagrams, then if I look at the subtraction A minus B, then I can view this as the difference between two tapes where one tape has a length of A and another tape has a length of B. And I can show that this way. So here's my tape A, here's my tape B, and here's my difference A minus B. And that's the difference that is the same as the value of that subtraction. Now, if I think about subtraction this way, the thing that I might notice here is if I increase the length of both tapes by the same amount, that difference doesn't change. So that increase in the length of both tapes doesn't change the difference. And so what does that do for us? Well, one of the things it does for us is now this difference A minus B is the same as the difference also between A plus K and B plus K. So I can run those together. And that's a useful transformation because it's possible that this new number I'm subtracting may be easier to work with than the old number I was subtracting. And in particular, if A plus K or B plus K is a benchmark number, then we have a relatively easy way of performing that computation. So, for example, let's say I want to subtract 8,014 and 1,997. And so what I can view is, well, 1,997 is pretty close to this benchmark number 2,000. In fact, it's just three away from that. So if I increase this by three, I get a number that's much easier to work with. And so what that suggests is I can add three to both terms. I could lengthen both tapes by three. And so this 8,014 minus 1,997 will add three to both the minuend and the subterhend, the thing I'm subtracting from. And so now I have the new subtraction 8,017 minus 2,000. And this is far easier to compute. That's going to be 6,017.